The present invention relates to a servovalve, which is also generally known as a fluid control valve, for controlling fluid flow and pressure in response to an electrical control signal.
By way of background, servovalves and systems utilizing servovalves are well known in the art. The prior art includes a double fixed orifice and nozzle-flapper valve, which is also known as a double nozzle-flapper valve and such valve is used to control the position of a spool valve by directing pressurized fluid to opposite ends of the spool valve. The double nozzle-flapper valves of the prior art were deficient in the sense that the flapper arrangement therein permitted continuous fluid flow through the valve, from the source to the reservoir, even when the valve was not energized, and this resulted in wasting the power required to produce the pressurized fluid. In addition, in prior types of systems utilizing a double nozzle-flapper valve, even when the servovalve was not electrically energized, pressurized fluid, at about 20% to 50% of the system pressure, was directed to opposite ends of the spool valve to cause it to remain in a neutral position. However, to shift the spool valve, additional pressurized fluid had to be directed to one end of the spool valve, and this pressurized fluid had to counteract the existing pressurized fluid at the other end of the spool valve. Thus, the differential pressure across prior spool valves was limited to 75%-80% of the supply pressure because pressure was acting on both ends of the spool. This required the system to operate at relatively higher pressures in order to achieve a given force to cause movement of the spool valve. Furthermore, in prior systems employing servovalves, because of the fact that fluid pressure was applied to opposite ends of the spool valve to center it, there could be no manual override of the spool without overcoming the force due to pressurized fluid on the ends of the spool valve. Furthermore, prior systems employing double nozzle-flapper valves were not "fail-safe". In this respect, since pressurized fluid was applied to opposite ends of the spool valve at all times, if a leak occurred in the conduits leading to one end of the spool valve, there would be a loss of pressure and the valve would shift. Additionally, if the spool valve housing experienced leakage, there would be a continuing flow of pressurized fluid to the housing, and such flow would carry impurities with it which would detrimentally affect the spool valve, as by causing undesired friction and possibly even clogging it against movement. Furthermore, in prior servovalve constructions the gain could not be adjusted by effectively varying the configuration of the armature after the servovalve was assembled. It is with overcoming the foregoing deficiencies of prior art servovalves that the present invention is concerned.